Set decoration warehouse (or so)

Some weeks ago I went with Lapin, Sagar and Pierre Amoudry to visit (and draw of course) one of the most amazing and weird places I've ever seen. Imagine an enormous 3 flat building full –I mean full as a can of sardines– of everything you could ever need for every kind of movie or stage set, from any sort of furnishing or lamp, to ancient maps, army radios, butcher knives, paper dolls, venetian masks, torture tools, musical instruments, chinese umbrellas, hats, stoves, umbrellas, tackles, coffins... absolutely everything!
I still wonder how could they know where any item (let's say) could be when they rented their stuff for films such as Biutiful or Vicky Cristina Barcelona.